Continuous mining machine with oscillating rotary cutter heads



Nov. 21, 1967 E. M. ARENTZEN CONTINUOUS MINING MACHINE WITH OSCILLATING ROTARY CUTTER HEADS Filed Aug. 5, 1964 6 Sheets-Sheet 1 R 0 w M N E/NAR M. ARENTZEN A Horneys Nov. 21, 1967 E. M. ARENTZEN CONTINUOUS MINING MACHINE WITH OSCILLATING ROTARY CUTTER HEADS GSheets-Sheet a FiledAug. 5, 1964 A r tarneys Nov. 21, 1967 E. M. ARENTZEN CONTINUOUS MINING MACHINE WITH OSCILLATING ROTARY CUTTER HEADS 6 Sheets-Sheet Filed Aug. 5, 1964 nv v5 ro/a E/NAR u. AREIVTZE/V} y M,

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Attorneys Nov. 21, 1967 E. M. ARENTZEN 6 Sheets-Sheet 5 Filed Aug. 5, 1964 INVENTOR.

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A/farneys Nov. 21, 1967 E. M. ARENTZEN CONTINUOUS MINING MACHINE WITH OSCI LLATING ROTARY CUTTER HEADS 6 Sheets-Shegt 6 Filed Aug. 5, 1964 n: ELI

A r forneys United States Patent 3,353,871 p CONTINUOUS MINING MACHINE WITH OSCIL- LATING ROTARY CUTTER HEADS Einar M. Areutzen, Charleroi, Pa., assig'nor to Lee-Norse Company, Charleroi, Pa.,- a corporation of Delawa're Filed Aug. 5, 1964, Ser. No. 387,583 16 Claims. (Cl. 299-71) This invention is for a continuous mining machine with hydraulically oscillated cutter supporting arms designed for the mining of minerals from the working face of a seam.

The instant invention is for an improvement in the continuous mining machine disclosed in United States Patent No. 2,695,164, granted to me on November 23, 1954. The machine is constructed primarily for the mining of coal, but it is applicable to the mining of other materials. By way of illustration, however, it will be described specifically in connection with the mining of coal.

In my patent above referred to, the machine has a mobile chassis having a wide sup-porting boom at its forward end that may be moved selectively under manual control in a vertical arc and on which are two arms, one at each side of the longitudinal axis of the machine, that are oscillated simultaneously across the boom in a generally horizontal arc. Each arm has a rotating cutter head at its outer end that rotates about a horizontal axis. As the machine engages the working face in the mine, the cutter heads rotate, digging and breaking out the coal or other mineral, while the arms swing toward and away from each other. At the start the boom is generally elevated so that the cutters sump into the coal seam at the roof for such distance as the operator desires. Then with the cutter heads revolving and being moved simultaneously toward and away from each other by the oscillating arms, the boom is lowered toward the mine floor. Simultaneous opposed movement of the arms is desirable so that the cutting forces at the front of the machine are balanced. The wide amplitude through which the arms move enables the entry or tunnel to be much wider than the machine.

The cutter heads of the respective arms are rotated by separate motors mechanically connected to operate in synchronism on each side of the machine through gears and separate drive shafts with universal joints therein, and oscillation of the cutter arms, as fully described in said patent, is effected by crank discs on the respective arms driven through gearing from the respective cutter head drives. Each crank disc has an eccentric crank pin. 0

Separate links pivotally anchored to a fixed pivot midway between the two arms extend oppositely from the pivot and each engages one of the crank pins on said discs, so that as the discs revolve, the arms are caused to move toward and away from the fixed pivot, that is, toward and away from each other.

While this is a highly satisfactory machine and introduced a new concept in continuous miners, it is apparent that the are through which the arms swing is fixed and cannot be changed where mining conditions require a tunnel or working face of narrower width and it was not possible to rotate the cutter heads Without also oscillating the arms. Both crank discs must rotate in exact isochronism so that a cross drive between the two motors mechanically connected them, as above referred to, to keep them synchronous. This resulted in a condition where one of the two motors could fail without the operator being immediately aware of it and impose the work entirely on the other motor.

Moreover, the gearing so provided between the two motors and between each motor and its cutter head and its rotating crank disc is heavy, expensive, and provides no cushion to'absorb shock when abnormal formations in the coal or other mineral are encountered. This not infrequently resulted in excessive wear and crank pin breakage. While this may be readily repaired, it results in down time and interferes with scheduled operations. This was especially true as larger machines were built.

The present invention is for a machine organized and operating in a similar manner, but hydraulic cylinder means operated by pumps driven .by the same motors that rotate the cutter head is utilized to effect the oscillatory motion of the cutter arms instead of a mechanical linkage. This eliminates the need for gearing interconnecting the'two motors as with the rotating disk-arrangement of my patent; it allows the amplitude. of the are through whichthe arms swingzto be changed, and since the motors are not connected the rotation of either. cutter head may be stopped by stopping its motor; and: if either motor should for any reason fail, the operator is made immediately aware of it because the cutter head which it drives stops rotating- With such a hydraulic system, pressure relief valve means may bypass the operating fluid where rock inclusions or other conditions which might overstress the parts are encountered, thus affording a safety'factor lacking in a straight mechanical drive for oscillating the arms.

It is a principal object of the present invention to provide a mining machine of the oscillating cutter arm type with hydraulically oscillated arms on which the cutter heads are carried.

Another object is the provision of a continuous mining machine having a hydraulic operating system including overload relief valve means to protect the machine against damage when unusual conditions are encountered.

Still another object is the provision of a continuous mining machine having a compact and effective hydraulic power system for synchronous oscillation of cutter head arms.

A further object is to provide a mining machine having a hydraulic system for oscillation of arms with cutter heads carried thereby which are rotated by independent motors whereby the failure of a motor stops the rotation of its associated head although the arms may continue to be oscillated by the one motor drive remaining in operation.

Another object is the provision of a mining machine having a hydraulic system for oscillation of arms, which may be adjusted to vary the amplitude of the arc through which the arms swing.

A complete understanding of the instant invention may be had from the following detailed description of a specific embodiment thereof when read in conjunction with the appended drawings, wherein:

FIG. 1 is a general plan view of the machine showing the overall arrangement of the various parts;

FIG. 2 is a side elevational view of the machine positioned for operation at the working face of the mine, the cutter heads being here schematically indicated as circles;

FIG. 3 is a longitudinal vertical section of a portion of the boom with a hydraulic cylinder and piston mechanism for oscillating the cutter arms;

FIG. 4 is a top plan view of the same portion of the boom with the cover removed;

FIG. 5 is a longitudinal vertical section in the line VV of FIG. 4;

FIG. 6 is an end elevation of the mechanism shown in FIG. 4 as viewed from the left end of FIG. 4;

FIG. 7 is a similar elevation as viewed from the right hand end of FIG. 4;

FIG. 8 is a transverse section through the cylinder and cross head in the plane of line VIIIVIII of FIG. 5

FIG. 9 is a schematic diagram of the hydraulic circuit; and

FIG. 10 is a top plan view of one of the cutter arms and its drive.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, FIGS. 1 and 2 show general assembly views of the continuous miningmachine designated generally as 11. As in my patented machine, the general assembly includes a chassis 12 which is mounted on crawlers 13. A gathering head 14 is located at the front end of the machine 11 with a conveyor 15 for receiving coal from the gathering head to carry it rearwardly for discharge.

On the forward end of the chassis 12 above the gathering head 14 is a boom 16 hinged at its downwardly offset rear end to the chassis for movement about a horizontal axis. This boom, which at its forward end extends across the full width of the machine supports two cutter carrying arms or carriers 18 one at each side of the center of the machine. These arms have their forward ends extending beyond the boom. At the outer end of each arm is a gear casing 19 that supports a cutter head 19, the cutter head having two spaced cutter wheels on a cross shaft 19a (see FIG. 10), one cutter wheel at each side of the housing 19, being generally that shown in my said patent. The inner end of each arm is pivoted for universal movement in a gear casing and universal joint housing 20. Each arm has a guide at 18a that is grooved to fit over a curved guide strip 16a at the front of the boom and by which the arm is slidably supported for horizontal movement and held against vertical movement relative to the boom.

The drive for rotating each of the rotary cutter heads 19 is from separate motors 21 which are supported on the boom 16. Each motor is directly coupled to the rotary head which it drives through a drive shaft and gears, as hereinafter more fully described.

This part of the machine so far described conforms generally, except as to certain changes not here material, to my previous patent. According to this invention, a fluid pressure operated mechanism comprising a cylinder and piston, one of which reciprocates relatively to the other is provided to oscillate the cutter head carrying arms. As here shown, the fluid pressure mechanism includes a reciprocating or travelling cylinder 22 with a cross-head 23 fixed thereon which is made to reciprocate on a fixed piston rod 24. On this rod is a stationary piston 25 positioned within the cylinder (see FIGS. 1, 3 and 4).

A pilot valve operating rock shaft 26 is rotatably supported in bearings 26a fixed to the boom, this shaft being positioned centrally above the cylinder 22 and extending lengthwise above it. On top of the cross head 23 are two camming strips 27a and 2712, one of these strips being at each side of and below the rod 26. Strip 27a is beveled at its forward or right hand end as viewed in FIGS. 4 to 8 and the other strip is similarly beveled at its rear or left end. At spaced distances on the shaft are rocker arms 28a and 28b, 28a being selectively adjustable to different locations in which it may be fixed near the forward end of the rock shaft whereas 28b is near the rearmost limit of travel of the yoke. Arm 2811 projects into the path of travel of caniming strip 27a and 28b into the path of travel of the camming strip 27b. When the cylinder and yoke 23 move forwardly, that is, to the right in the drawings, the inclined or beveled end of strip 27a rides under the projecting end of the arm 28a, which is in the form of an inserted ball, and lifts it, rocking the shaft in one direction, arm 23b at that time being clear of its camming strip 2712. When the cylinder travels in the reverse direction, the beveled end of strip 27b, riding under arm 28b lifts it, rocking the shaft back to its former position.

Near the rear end of the rock shaft 26 is an arm 26b to which is attached a link 26c that is connected to the stem of a pilot valve 22 so that as t e shaft is rocked one way and then the other the pilot valve is moved back and forth at the limits of travel of the cylinder to reverse the fluid pressure and reverse the travel of the cylinder as will be hereinafter more fully explained.

As best shown in detail in FIG. 3, the fixed piston rod 24 is hollow and it has a tube or pipe 31 concentrically positioned therewithin, one end of which is secured to the stationary piston 25 and its other end is fastened to a union 32. It provides a passage through which fluid under pressure is introduced into the cylinder to effect reciprocation thereof in one direction. The conduit 31 opens into a passage 33 through the union to establish a flow path to a central passage 34 through the fixed piston 25. Radial apertures 35 are provided through the piston rod 24 to the right of the piston 25, as viewed in FIG. 3, whereby fluid may be ported into a chamber 36. A bleed passage 37 is provided in the stationary piston which communicates with the central bore 34 of the piston 25 and the chamber 36 into which fluid under pressure is directed to initiate movement of the cylinder 22 to the right, as viewed in this figure. The radial apertures 35 are uncovered after a short distance of travel of the cylinder 22 to the right whereupon fluid is introduced into the chamber 36 to then continue driving the cylinder to the right at a greater speed.

The annular space 38 between the conduit 31 and the inner wall of the hollow piston rod 24 serves as a passage through which fluid is introduced through an inlet port 39 from a separate circumferential passage 39a in the union 32 to radial openings 41 provided through the rod adjacent the left side of the piston as seen in FIG. 3, and thence to the cylinder chamber 42 to the left of the stationary piston '25, first through bleed port 43 and then via the radial openings 41, as viewed in FIG. 3, it being understood that at this time the cylinder is at the opposite limit of its'travel from that shown in FIG. 3 so that ports 41 are then Within the packing sleeve 41a at the left end of the cylinder. The corresponding sleeve at the other end of the cylinder is designated 35a. Consequently, when fluid under pressure is introduced into the chamber 42 on the left of the fixed piston, the traveling cylinder 22 is driven to the left, and, similarly, when fluid is ported to the chamber 36 on the right of the fixed piston, the traveling cylinder is forced to the right.

Fluid from the chamber 36 on the right of the piston is expelled through the same channels above described, through which it is introduced, and this is also true for chamber 42.

Motion is transmitted to the cutter arms 18 from the cross-head 23 on the traveling cylinder through links 56 pivotally interconnected to the arms 18 at 56a, and with the cross-head through a yoke and pin assembly 57, one such link being at each side of the cross-head. Thus, when the cross-head is moved toward the front end of the machine 11, the links 56 increase the angle between the cutter arms 18 to effect a simultaneous horizontal arcuate movement of the arms away from each other toward the outer sides of the machine. Similarly, when the cross-head is moved toward the rear of the machine, the arms are drawn toward the center of the machine, reducing the angle between the arms pulling them together toward the: center. The amplitude of the arcs through which the arms swing, that is, the throw of the arms, is determined by the length of travel of the cylinder and cross-head and if no fluid pressure is supplied to the cylinder, the arms; will remain fixed in any position while either or both, cutter heads 19 may revolve. The arms 18 move equally' and in opposite directions in synchronism as in my earlier' patent, but the arms may be held stationary while the cutters are revolving, which is an added desirable feature.

The hydraulic system effecting the reciprocation of the cylinder in the manner above described may best be understood by reference to the flow diagram shown in FIG. 9. It should first be pointed out that the element marked (t0. and. labelled tank appearing at the top and bottom of the left side of FIG. 9 is the same vessel or reservoir but for purpose of clarity the intake of the fluid system indicated at 61 is at the top of the diagram and the dis charge represented by diffuser 62 is at the bottom of the diagram. The tank 60 also appears elsewhere in the diagram to indicate the same vessel.

A motor 63 on one side of the machine back of motor 21 (see FIG. 1) drives a pump 64 that circulates oil from the reservoir to a cooler 65 and from the cooler the oil flows through a filter 66 into pipe 67. Oil that is not needed for the operation of the hydraulic mechanism flows back through a pressure relief valve 68 into the diffuser 62 in the tank 60.

Each of the two motors 21 is geared in gear box 20 to a constant volume high pressure pump, these pumps being designated 69a and 6%. Oil from pipe 67 flows through branch pipe 70 to the intake of pump 69a and from the pipe 67 through branch pipe 71 to the intake of pump 6%. Pump 69a discharges high pressure fluid through pipe 72 to a bypass and reversing valve assembly, designated generally at 73, and pump 69b discharges high pressure oil through pipe 74 to the same unit 73 where the output of the two pumps combine.

Part of the high pressure oil from unit 73 is carried from this unit through pipe 75 to a conventional on and off valve 76, which has a manual operating lever movable from a stop position which blocks the flow of fluid to a start position where it is open to the passage of fluid therethrough into line 77. This line has a branch 78 leading to a prepressured accumulator 79, and a branch 80 which connects both line 77 and the accumulator to the single inlet port of the conventional spool type pilot valve 29 heretofore referred to. This pilot valve upon the rocking of the rock shaft 26 in one direction and then the other, passes high pressure fluid alternately into pipes 81 and 82, to reciprocate a conventional fluid pressure operated reversing valve 83. When fluid is flowing through pipe 81 to one side of the reversing valve, fluid is expelled through pipe 82 and the pilot valve to pipe 84 to return to the tank 60, and vice versa. In the diagram fluid pressure is in line 81, for which reason it is shown with arrows, while exhaust liquid is flowing through pipe 82., to which no arrows are applied. When pilot valve 29 is reversed, this condition would be reversed and 82 would become the pressure line and 81 the exhaust.

The reversing valve distributes the high pressure fluid from the two pumps 69a and 69b, other than that used in the pilot valve circuit and that required for certain accessory functions, to the cylinder 22. With the parts in the position shown in the diagram, high pressure fluid is passing through pipe 84 into passage 33 to move the cylinder to the right to spread the arms 28 while fluid in the space 42 to the left of the piston is exhausted through ports 39 to the circumferential passage 31 and connection 85 to pipe 86. The exhaust liquid from pipe 86 passes through the reversing valve and internal passages in the assembly 73 to line 87 and into the diffuser 62 in the tank 60.

When the reversing valve is moved in the other direction the pipe 84 becomes the exhaust pipe for the escape of oil from the right end of the cylinder and pipe 86 becomes the high pressure supply line to the left side of the cylinder.

In the assembly 73 there is a pressure relief valve 88 of known construction, such as a spring biased valve shunted across the high pressure and exhaust lines, so arranged as to bypass high pressure fluid from the two high pressure pumps to the exhaust line 87 when pressures exceed a predetermined maximum. It is a safety feature allowing the movement of the arms to stall before they are overstressed. For example, in moving together a rock or very hard slate may come between the arms, preventing their closing movement. In this case the relief valve opens, protecting the mechanism, particularly pivot pins for the arm reciprocating links from damage. Nevertheless the motors may continue to operate and rotate the cutters, and if the cutters gradually remove the obstruction, the arms will continue moving. Fluid under pressure is normally maintained above the pressure relief valve,- but when valve 76 is moved to stop 'positioii, pressure in line 77 is relieved with the liquid flowing back through this line to the tank whereupon pressure over the relief valve is vented through pipe 88' and check valve 88a to the line 77 so that when the handle of valve 60 is moved to stop position even though the pumps 69a and 695 are still operating, the effect of moving the stop and start valve is to relieve the pressure in line 77, allowing pressure in the relief valve to drop, thereby shunting the high pressure fluid to the reservoir to starve the pilot valve and reversing valve and the cylinder and piston means of operating pressure. The same movement of the stop and start valve will allow liquid in line 75 to flow to the reservoir or tank, so that the output of the pumps 69a and 69b, which operate as long as the motors 21 are operating, will be bypassed to the reservoir. When the stop and start valve is in the operating position, the output of the two high pressure pumps flows through this valve, as previously explained to establish normal high pressure in the relief valve and all other parts of the hydraulic system with which they communicate. The check valve 88 prevents any backflow of pressure from the accumulator into the relief valve such as might interfere with the quick stopping of the hydraulic mechanism. The system described facilitates the removal of entrapped air which presents a problem in a hydraulic system.

Remaining elements of the diagram pertain to lubrication, gauges and so forth not particularly involved here.

In FIG. 10 the general driving arrangement for one of the cutter heads and one of the high pressure pumps is shown. In this view 21 is one of the two motors hereinbefore described, the shaft of which extends into a gear box 20. Within the gear box this shaft has a pinion 21a which meshes with a gear 21b for driving the high pressure pump 69a. The same pinion also meshes with a gear 21c which transmits rotary motion through a universal joint to a shaft 18b that extends lengthwise of the cutter arm and on the forward end of which is a bevel pinion 180. This in turn meshes with a bevel gear 18d on a shaft 18e parallel with the shaft of the cutter head. This shaft in turn has spur gear 18f that meshes with a spur gear and the cutter head shaft. A balllike housing on the inner end of arm 18 surrounds the universal joint and provides the axis about which the arm pivots. Each motor 21 contributes equally to the power requirements for oscillating the cutter arms, as in my prior patent, eliminating different motors on opposite sides of the machine, or a separate motor for driving the high pressure fluid mechanism.

It may be noted that since the parts 35 and 41 close just before the full limit of travel of the cylinder is reached, the restricted passages 37 and 43 restrict the escape of the out-going liquid tending thereby to cushion the motion of the arms at the ends of their strokes in addition to gradually admitting fluid at the beginning of the stroke in the opposite direction.

With this arrangement, each of the main motors 21 drives a high pressure pump and also drives a cutter head on the arm adjacent which it is positioned. As previously explained, the cutter heads may thus be rotated Without the arms being reciprocated and either cutter head may be held against rotation while the other is turning. Since the two motors 21 are entirely independent, if one motor would fail, its cutter head would cease rotating thereby immediately informing the operator of the failure of the motor. The two arms 18 of course always move equally and oppositely through the same are and the power for moving them is derived from the motors 21 through the hydraulic system, but mechanical synchronization of the two motors is not required. An added advantage is that by adjusting the rocker arm 2811 on the shaft 26 the length of the arc may be varied as conditions in the mine may require.

It is manifest that the above-described embodiment of the invention is merely illustrative and that numerous modifications and revisions may be made within the :spirit and scope of the invention.

What is claimed is:

1. A mining machine comprising a chassis, a boom connected to the forward end of the chassis for vertical movement relative to the chassis, a pair of carriers mounted on the boom for horizontal side-by-side movement, a rotary cutter on the forward end of each carrier, a separate motor for driving each cutter, means operatively connecting each motor with the cutter which it drives, a fluid pressure mechanism including relatively movable cylinder and piston members, said fluid pressure mechanism being connected to said boom and to said carriers for horizontally oscillating said carriers simultaneously in opposition to one another, and a source of fluid pressure connected to supply pressure fluid to said fluid pressure mechanism to cause the latter to continuously oscillate said carriers during the normal operation of the mining machine, said source including a separate pump driven by each motor and a fluid pressure circuit for each pump connected in a common circuit with said fluid pressure mechanism through which fluid pressure is supplied to the fluid pressure mechanism.

2. A mining machine as in claim 1 wherein pressure relief means is connected in common to the pump circuits to by-pass high pressure fluid around the fluid pressure :mechanism such that the horizontal movement of both tOf said carriers is retarded in the event that the cutter of either carrier encounters abnormal resistance.

3. In a mining machine having a chassis with a boom :swingable about a horizontal axis at the forward end of the chassis, a pair of cutter carriers each pivotally :secured to the boom at its rear portion for arcuate travel :at their forward portion toward and away from the boom longitudinal centerline in opposition to effect a pincerllike action, a cutter mounted for rotation on the forward portion of each carrier, a separate drive motor for each cutter, fluid pressure motor means supported on the boom between the carrier and links interconnected to the fluid pressure motor means and pivotally to each carrier intermediate its forward and rear portions arranged to pull the carriers together into side-by-side relationship and then push the carriers apart whereby oscillation of the carriers in equal arcs of travel is effected, and means responsive to the movement of the carriers for reversing the travel at each limit of movement such that the carriers are continuously oscillated during the normal operation of the mining machine.

4. In a mining machine as in claim 3 wherein the fluid motor means is a reciprocating cylinder with a fixed piston, and fluid circuit means are provided for forcing the cylinder in opposite directions.

5. In a mining machine as in claim 4 wherein the fluid circuit means includes a pair of pumps each driven by one of the separate drive motors, and a hydraulic control circuit including a pilot valve operated by the fluid pressure motor means is provided for regulating the direction of flow to the motor means to force the cylinder alternately in opposite directions.

6. In a mining machine as in claim 5 wherein a pilot valve is provided in the control circuit, and means responsive to travel of the cylinder is provided for operat ing the pilot valve spool to control the direction of fluid from the pumps to either one side or the other of the fixed piston of the fluid motor, there being a pressure relief valve arranged to by-pass fluid around the cylinder piston when the resistance to movement of the carriers exceeds a predetermined amount.

7. In a mining machine as in claim 6 wherein a main valve is connected in common to the two pumps and to the fluid motor, the pilot valve being operatively con- 8 ected to the main valve for positioning of the main valve for the direction of fluid from the pumps through the main valve to either one or the other side of the piston to drive the cylinder in one direction or the other, and means responsive to the operation of the mechanism for operating the pilot valve.

8. A mining machine of the type having a chassis with a boom thereon at the front thereof movable in a vertical arc and having a pair of carriers thereon movable over the boom in a horizontal arc with cutters on the outer ends of the carriers rotatable about a horizontal axis and means for rotating the cutters characterized by the provision of a reciprocable hydraulic fluid pressure cylinder and piston means connected to the boom between the two carriers and connected to the two carriers for simultaneously moving said carriers equally and in opposite directions, and valve means controlled through the operation of the pressure cylinder means for reversing the movement of cylinder and piston means at the limits of travel of the carriers such that said carriers are moved continuously during the normal operation of the mining machine substantially in unison.

9. A mining machine as defined in claim 8 wherein the cutter on each carrier is driven by a separate motor and each cutter driving motor also drives a high pressure hydraulic pump, the output of said pumps being connected into a common circuit including the hydraulic fluid pressure cylinder and piston means and the valve means for controlling the operation thereof whereby both motors normally contribute equal power to driving the rotatable cutters while effecting the oscillation of the carriers.

10. A mining machine as defined in claim Q in which the common output circuit includes a manually operable stop and start valve having stop and start positions arranged to control the fluid pressure cylinder and piston means for rendering the same operative or inoperative while the motors may continue to rotate their respective cutters.

11. A mining machine as defined in claim 9 in which the common output circuit includes a manually operable stop and start valve having stop and start positions arranged to control the fluid pressure cylinder and piston means for rendering the same operative or inoperative While the motors may continue to rotate their respective cutters, the circuit alsoincluding a relief valve for bypassing high pressure fluid from the cylinder and piston means when the resistance to movement of the carrier exceeds a predetermined maximum.

12. A mining machine as defined in claim 9 in which the common output circuit includes a manually operable stop and start valve having stop and start positions arranged to control the fluid pressure cylinder and piston means for rendering the same operative or inoperative while the motors may continue to rotate their respective cutters, the circuit also including a relief valve for bypassing high pressure fluid from the cylinder and piston means when the resistance to movement of the carriers exceeds a predetermined maximum, the stop and start valve being connected to by-pass high pressure fluid through the relief valve in the stop position and to close such by-passing in the start position.

13. A mining machine as defined in claim 8 wherein the cylinder and piston means includes valving to check the speed of operation thereof near the opposite reciprocable limits of movement thereof.

14. A mining machine comprising a chassis, a boom connected to the forward end of said chassis for vertical movement relative to said chassis, a pair of carriers mounted on said boom for side-by-side horizontal movement, a rotary cutter connected to the forward end of each of said carriers, motor means connected to said cutters for rotatably driving said cutters, hydraulically operated motor means connected to said boom and to each of said carriers for horizontally oscillating said 16. A mining machine as defined in claim 14 wherein means is provided for controlling the horizontal movement of said carriers such that the horizontal movement of both carriers is retarded in the event that the cutter of either carrier encounters abnormal resistance to its horizontal movement.

References Cited UNITED STATES PATENTS Waite et a1. 37-185 Driehaus 299-1 Pitcher 173154 X Sibley 29971 Hlinsky 29971 Delli-Gatti 299-71 X Hlinsky 299-1 ERNEST R. PURSER, Primary Examiner. 

14. A MINING MACHINE COMPRISING A CHASSIS, A BOOM CONNECTED TO THE FORWARD END OF SAID CHASSIS FOR VERTICAL MOVEMENT RELATIVE TO SAID CHASSIS, A PAIR OF CARRIERS MOUNTED ON SAID BOOM FOR SIDE-BY-SIDE HORIZONTAL MOVEMENT, A ROTARY CUTTER CONNECTED TO THE FORWARD END OF EACH OF SAID CARRIERS, MOTOR MEANS CONNECTED TO SAID CUTTER FOR ROTATABLY DRIVING SAID CUTTERS, HYDRAULICALLY OPERATED MOTOR MEANS CONNECTED TO SAID BOOM AND TO EACH OF SAID CARRIER FOR HORIZONTALLY OSCILLATING SAID CARRIERS SIMULTANEOUSLY IN OPPOSITION TO ONE ANOTHER, AND MEANS FOR CAUSING SAID HYDRAULICALLY OPERATED MOTOR MEANS TO HORIZONTALLY OSCILLATE SAID CARRIERS CONTINUOUSLY DURING THE NORMAL OPERATION OF THE MINING MACHINE. 